A repetitive wave sampler in used to obtain instantaneous values on an unknown waveform having a known frequency of repetition and/or to reconstruct the unknown waveform. It operates on principles which take advantage of the fact that the signal being sampled has a known frequency of repetition.
A repetitive wave sampler can be used in conjunction with an analog to digital converter to sample and reconstruct an unknown waveform having a known frequency. Repetitive wave samplers can be used in many application. Such typical applications include laboratory and production testing of both analog and digital devices. During laboratory or production testing of a device, a known waveform is provided at the input of the device under test (D.U.T.) and it is desired to determine the output waveform. Many of the performance specifications of a device, such as output rise and fall times, overshoot etc., are determined in this manner. The known input waveform can be fed in at a known repetition rate such that the output of the device will be an unknown waveform but with a known repetition rate.
One method typical of the prior art of sampling repetitive waveforms is utilized in sampling oscilloscopes. Typically, a sampling oscilloscope operates on the principle of a stroboscope. A repetitive waveform of known frequency is sampled at a rate slightly slower than the rate of repetition of the waveform. In this manner each consecutive sample is taken at a point which progresses incrementally along the cycle of the waveform. The ratio between the sampling rate and the rate of repetition of the waveform will determine the number of samples obtained during one cycle of the repetitive waveform. The locus of points obtained in this manner, over the course of several cycles, can be displayed to reconstruct a replica of the unknown repetitive signal.
The accuracy of such circuits/samplers, however, leaves much to be desired. Any noise in the signal during sampling will distort the measurement at that point. Discrete circuit implementations of repetitive wave samplers are particularly prone to noise since external electrical couplings produce substantial noise in the circuit and discrete circuits require substantially longer conductor lengths (wires) than integrated circuit implementations. Decreasing the length of the conductors in the circuit is particularly helpful in reducing the inherent inductance of the wires which can seriously diminish the accuracy of the device.
Moreover, the samplers typically have a significant amount of input capacitance. This input capacitance, coupled with the inherent inductance from the wires, may cause the circuit to exhibit resonances which may significantly reduce the accuracy of the measurement. The probe input capacitance is particularly bothersome in sampling high frequency signals because it can easily load the circuit by providing a parasitic, low impedance path to ground. For these reasons, integrated circuit implementations of wave samplers, particularly high frequency wave samplers, is highly desirable.
Further, the prior art means for sampling waveforms are limited in terms of the maximum bandwidth of the signal which can be sampled. As the bandwidth of the signal to be sampled increases, the size, power consumption and cost of the apparatus necessary to perform the sampling function increases dramatically. Typically, circuits capable of sampling a waveform having a bandwidth of 100 MHz or higher consume several watts of power, require a large number of connection pins (12-24 or more pins) and are limited in both the input range and the resolution available.
Therefore, it is an object of the present invention to provide an improved repetitive wave sampler.
It is another object of the present invention to provide a repetitive wave sampler having high resolution.
It is a further object of the present invention to provide a repetitive wave sampler capable of sampling waveforms having a bandwidth of 350 MHz and greater.
It is yet another object of the present invention to provide a high speed repetitive wave sampler having low power consumption.
It is further object of the present invention to provide a high speed wave sampler of small size.
It is another object of the present invention to provide a high speed repetitive wave sampler having low input capacitance.
It is one more object of the present invention to provide a high speed repetitive wave sampler having a large input range.
It is still another object of the present invention to provide a high speed repetitive wave sampler having low input inductance.
It is yet another object of the present invention to provide a high speed repetitive wave sampler having inherent immunity to uncorrelated noise.
It is one more object of the present invention to provide a high speed repetitive wave sampler having low sensitivity to inductively and capacitively coupled noise.